A sector is a portion of a circle bounded by two radii and the arc joining their extremities. It is thus a form of triangle with a covered base. In the figure the portion is a sector. Arc is called the arc of the sector and is called the angle of the sector. The area of a sector of a circle is equal to a fraction of the area of the circle determined by dividing the size of the angle by. Thus, if the angle of the sector is , the area of the sector is or the area of the circle, that is, i.e., the area of a sector bears that portion to the area of the circle which its angle bears to right angles i.e., .
(a) If the angle is given in degrees, say, then
Example: Its area is equal to Since radius cm Therefore Square
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